After Thin Film Transistor-Liquid Crystal Display (TFT-LCD) emerges, the AMOLED display panel has become a new generation display panel with the most promising future. Compared with traditional liquid crystal display panel, the AMOLED panel has the advantages of thin, light, and simple structure, self-luminous without backlight, wide viewing angle, beautiful and colorful images, and bendable.
In general, each of the pixel circuits of the AMOLED panel is equipped with Low Temperature Poly-Si Thin Film Transistor (LT P—Si TFT) with switching function and a charge storage capacitor. In addition, the peripheral driving circuit and the display array of the AMOLED panel are integrated in the same glass substrate.
During the manufacturing of the AMOLED panel, laser scanning is widely used in the crystallization. Due to the instable power of the laser beam, the Thin Film Transistors formed in the scanning lines obtained by the scanning of the laser beam may have different threshold voltages, and thus the problem of non-uniform image qualities in a plurality of pixel regions could be caused.
FIG. 1 is a structural diagram of the pixel circuit 100 (with two transistors and one capacitor; 2T1C) in the current Organic Light Emitting Diode (OLED) display technology. The method for driving the pixel circuit 100 is as follows. When the scanning line SL receives the scanning signal Vscan and therefore the Thin Film Transistor T1 is turned on, the data line DL receives the data signal Vdata, so that the data signal Vdata is stored in the capacitor Cc through the Thin Film Transistor T1. When the scanning line SL receives the scanning signal Vscan and therefore the Thin Film Transistor T1 is turned off, the Thin Film Transistor T2 is turned on continuously, so that the voltage stored in the capacitor Cc is applied to the OLED of the pixel circuit. In this case, the driving current Ioled which drives the OLED to emit light can be generated.
However, in the above pixel circuit, since the Thin Film Transistor T2 is under the state of positive bias driving for a long time, the threshold voltage Vth of the Thin Film Transistor T2 would drift. Once the drifting of the threshold voltage Vth of the Thin Film Transistor T2 happens, the driving current Ioled flowing through the OLED would be affected directly. Consequently, for each pixel circuit in the OLED display technology, the currents flowing through the OLEDs of the respective pixel circuits and reflecting the same data signal Vdata would be different from one another. Under such circumstances, the gray-scales of the OLEDs of the respective pixel circuits would be different from one another, and thus the display uniformity of the OLED panel would be affected.
To solve the above problem, a pixel circuit having a structure of three transistors and one capacitor (3T1C) with compensation function is proposed in the prior art. However, the above pixel circuit having a 3T1C structure can only be used in large sized OLED display device driven through Simultaneous Emission (SE) mode, but cannot be used in OLED display device driven through Progressive Emission (PE) mode.
Therefore, how to solve the aforesaid problem has become an effort demanding task in the industry.